本文原创
vector 是 STL 中使用得最频繁的容器，其所使用的内存大小是动态扩展的，且分配和回收完全无需调用者管理，弥补了静态数组某些时候内存开销过大的缺陷。
头文件 stl_vector.h 定义了 vector 类，但未定义 vector<bool> 特化实现。
vector 是一个派生类，其基类定义及设置基类的好处如下：
// The vector base class serves two purposes. First, its constructor and
// destructor allocate (but don't initialize) storage. This makes exception
// safety easier. Second, the base class encapsulates all of the differences
// between SGI-style allocators and standard-conforming allocators.
template <class _Tp, class _Alloc>
class _Vector_base
{
public:
typedef _Alloc allocator_type; // _Alloc 一般是 alloc
allocator_type get_allocator() const { return allocator_type(); }
_Vector_base(const _Alloc&) : _M_start(0), _M_finish(0), _M_end_of_storage(0) {}
_Vector_base(size_t __n, const _Alloc&) : _M_start(0), _M_finish(0), _M_end_of_storage(0)
{
_M_start = _M_allocate(__n);
_M_finish = _M_start;
_M_end_of_storage = _M_start + __n;
}
~_Vector_base() { _M_deallocate(_M_start, _M_end_of_storage - _M_start); }
protected:
_Tp* _M_start; // 存储元素的起始位置
_Tp* _M_finish; // 存储元素的末尾位置
_Tp* _M_end_of_storage; // 存储容量的末尾位置
typedef simple_alloc<_Tp, _Alloc> _M_data_allocator; // simple_alloc 是 allocator adaptor
_Tp* _M_allocate(size_t __n) { return _M_data_allocator::allocate(__n); }
void _M_deallocate(_Tp* __p, size_t __n) { _M_data_allocator::deallocate(__p, __n); }
};
基类较为简单，负责内存的分配和回收。下面分析 vector，无形参采用默认值的成员函数在此省略：
template <class _Tp, class _Alloc = alloc>
class vector : protected _Vector_base<_Tp, _Alloc>
{
__STL_CLASS_REQUIRES(_Tp, _Assignable);
private:
typedef _Vector_base<_Tp, _Alloc> _Base;
public:
typedef _Tp value_type;
typedef value_type* pointer;
typedef const value_type* const_pointer;
typedef value_type* iterator;
typedef const value_type* const_iterator;
typedef value_type& reference;
typedef const value_type& const_reference;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef reverse_iterator<iterator> reverse_iterator;
typedef reverse_iterator<const_iterator> const_reverse_iterator;
typedef typename _Base::allocator_type allocator_type;
allocator_type get_allocator() const { return _Base::get_allocator(); }
protected:
#ifdef __STL_HAS_NAMESPACES
using _Base::_M_allocate;
using _Base::_M_deallocate;
using _Base::_M_start;
using _Base::_M_finish;
using _Base::_M_end_of_storage;
#endif /* __STL_HAS_NAMESPACES */
protected:
void _M_insert_aux(iterator __position, const _Tp& __x);
public:
iterator begin() { return _M_start; }
const_iterator begin() const { return _M_start; }
iterator end() { return _M_finish; }
const_iterator end() const { return _M_finish; }
reverse_iterator rbegin() { return reverse_iterator(end()); }
const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); }
reverse_iterator rend() { return reverse_iterator(begin()); }
const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
size_type size() const { return size_type(end() - begin()); }
size_type max_size() const { return size_type(-1) / sizeof(_Tp); }
size_type capacity() const { return size_type(_M_end_of_storage - begin()); }
bool empty() const { return begin() == end(); }
reference operator[](size_type __n) { return *(begin() + __n); }
const_reference operator[](size_type __n) const { return *(begin() + __n); }
#ifdef __STL_THROW_RANGE_ERRORS
void _M_range_check(size_type __n) const
{
if (__n >= this->size())
__stl_throw_range_error("vector");
}
reference at(size_type __n) { _M_range_check(__n); return (*this)[__n]; }
const_reference at(size_type __n) const { _M_range_check(__n); return (*this)[__n]; }
#endif /* __STL_THROW_RANGE_ERRORS */
/* example: vector<int> v; */
explicit vector(const allocator_type& __a = allocator_type()) : _Base(__a) {}
/* example: vector<int> v(5,0); */
vector(size_type __n, const _Tp& __value,
const allocator_type& __a = allocator_type()) : _Base(__n, __a)
{ _M_finish = uninitialized_fill_n(_M_start, __n, __value); }
/* example: vector<int> v(5); */
explicit vector(size_type __n) : _Base(__n, allocator_type())
{ _M_finish = uninitialized_fill_n(_M_start, __n, _Tp()); }
/* example: vector<int> v(v0); */
vector(const vector<_Tp, _Alloc>& __x) : _Base(__x.size(), __x.get_allocator())
{ _M_finish = uninitialized_copy(__x.begin(), __x.end(), _M_start); }
/* example: vector<int> v(v0.begin(), v0.end()); */
vector(const _Tp* __first, const _Tp* __last,
const allocator_type& __a = allocator_type()) : _Base(__last - __first, __a)
{ _M_finish = uninitialized_copy(__first, __last, _M_start); }
~vector() { destroy(_M_start, _M_finish); }
vector<_Tp, _Alloc>& operator=(const vector<_Tp, _Alloc>& __x);
void reserve(size_type __n)
{
if (capacity() < __n)
{
const size_type __old_size = size();
iterator __tmp = _M_allocate_and_copy(__n, _M_start, _M_finish);
destroy(_M_start, _M_finish);
_M_deallocate(_M_start, _M_end_of_storage - _M_start);
_M_start = __tmp;
_M_finish = __tmp + __old_size;
_M_end_of_storage = _M_start + __n;
}
}
// assign(), a generalized assignment member function. Two
// versions: one that takes a count, and one that takes a range.
// The range version is a member template, so we dispatch on whether
// or not the type is an integer.
void assign(size_type __n, const _Tp& __val) { _M_fill_assign(__n, __val); }
void _M_fill_assign(size_type __n, const _Tp& __val);
reference front() { return *begin(); }
const_reference front() const { return *begin(); }
reference back() { return *(end() - 1); }
const_reference back() const { return *(end() - 1); }
void push_back(const _Tp& __x)
{
if (_M_finish != _M_end_of_storage) // size() != capacity()
{
construct(_M_finish, __x);
++_M_finish;
}
else
_M_insert_aux(end(), __x);
}
void swap(vector<_Tp, _Alloc>& __x)
{
__STD::swap(_M_start, __x._M_start);
__STD::swap(_M_finish, __x._M_finish);
__STD::swap(_M_end_of_storage, __x._M_end_of_storage);
}
iterator insert(iterator __position, const _Tp& __x)
{
size_type __n = __position - begin();
if (_M_finish != _M_end_of_storage && __position == end())
{
construct(_M_finish, __x);
++_M_finish;
}
else
_M_insert_aux(__position, __x);
return begin() + __n; // insert 后，返回的 iterator 位置不后移
}
/* range insert 版本 */
void insert(iterator __position, const_iterator __first, const_iterator __last);
void insert (iterator __pos, size_type __n, const _Tp& __x)
{ _M_fill_insert(__pos, __n, __x); }
void _M_fill_insert (iterator __pos, size_type __n, const _Tp& __x);
void pop_back()
{
--_M_finish;
destroy(_M_finish);
}
iterator erase(iterator __position)
{
if (__position + 1 != end())
copy(__position + 1, _M_finish, __position);
--_M_finish;
destroy(_M_finish);
return __position;
}
iterator erase(iterator __first, iterator __last)
{
iterator __i = copy(__last, _M_finish, __first);
destroy(__i, _M_finish);
_M_finish = _M_finish - (__last - __first);
return __first;
}
void resize(size_type __new_size, const _Tp& __x)
{
if (__new_size < size())
erase(begin() + __new_size, end());
else
insert(end(), __new_size - size(), __x);
}
void resize(size_type __new_size) { resize(__new_size, _Tp()); }
void clear() { erase(begin(), end()); }
protected:
iterator _M_allocate_and_copy(size_type __n, const_iterator __first,
const_iterator __last)
{
iterator __result = _M_allocate(__n);
__STL_TRY {
uninitialized_copy(__first, __last, __result);
return __result;
}
__STL_UNWIND(_M_deallocate(__result, __n));
}
};
类外定义的成员函数：
template <class _Tp, class _Alloc>
void vector<_Tp, _Alloc>::_M_insert_aux(iterator __position, const _Tp& __x)
{
if (_M_finish != _M_end_of_storage)
{
construct(_M_finish, *(_M_finish - 1));
++_M_finish;
_Tp __x_copy = __x;
copy_backward(__position, _M_finish - 2, _M_finish - 1);
*__position = __x_copy;
}
else
{
const size_type __old_size = size();
const size_type __len = __old_size != 0 ? 2 * __old_size : 1;
iterator __new_start = _M_allocate(__len);
iterator __new_finish = __new_start;
__STL_TRY {
__new_finish = uninitialized_copy(_M_start, __position, __new_start);
construct(__new_finish, __x);
++__new_finish;
__new_finish = uninitialized_copy(__position, _M_finish, __new_finish);
}
__STL_UNWIND((destroy(__new_start,__new_finish), _M_deallocate(__new_start,__len)));
destroy(begin(), end());
_M_deallocate(_M_start, _M_end_of_storage - _M_start);
_M_start = __new_start;
_M_finish = __new_finish;
_M_end_of_storage = __new_start + __len;
}
}
template <class _Tp, class _Alloc>
void vector<_Tp, _Alloc>::_M_fill_assign(size_t __n, const value_type& __val)
{
if (__n > capacity())
{
vector<_Tp, _Alloc> __tmp(__n, __val, get_allocator());
__tmp.swap(*this);
}
else if (__n > size())
{
fill(begin(), end(), __val);
_M_finish = uninitialized_fill_n(_M_finish, __n - size(), __val);
}
else
erase(fill_n(begin(), __n, __val), end());
}
template <class _Tp, class _Alloc>
void vector<_Tp, _Alloc>::_M_fill_insert(iterator __position, size_type __n,
const _Tp& __x)
{
if (__n != 0)
{
if (size_type(_M_end_of_storage - _M_finish) >= __n)
{
_Tp __x_copy = __x;
const size_type __elems_after = _M_finish - __position;
iterator __old_finish = _M_finish;
if (__elems_after > __n) {
uninitialized_copy(_M_finish - __n, _M_finish, _M_finish);
_M_finish += __n;
copy_backward(__position, __old_finish - __n, __old_finish);
fill(__position, __position + __n, __x_copy);
}
else
{
uninitialized_fill_n(_M_finish, __n - __elems_after, __x_copy);
_M_finish += __n - __elems_after;
uninitialized_copy(__position, __old_finish, _M_finish);
_M_finish += __elems_after;
fill(__position, __old_finish, __x_copy);
}
}
else
{
const size_type __old_size = size();
const size_type __len = __old_size + max(__old_size, __n);
iterator __new_start = _M_allocate(__len);
iterator __new_finish = __new_start;
__STL_TRY {
__new_finish = uninitialized_copy(_M_start, __position, __new_start);
__new_finish = uninitialized_fill_n(__new_finish, __n, __x);
__new_finish
= uninitialized_copy(__position, _M_finish, __new_finish);
}
__STL_UNWIND((destroy(__new_start,__new_finish), _M_deallocate(__new_start,__len)));
destroy(_M_start, _M_finish);
_M_deallocate(_M_start, _M_end_of_storage - _M_start);
_M_start = __new_start;
_M_finish = __new_finish;
_M_end_of_storage = __new_start + __len;
}
}
}
template <class _Tp, class _Alloc>
void vector<_Tp, _Alloc>::insert(iterator __position,
const_iterator __first, const_iterator __last)
{
if (__first != __last)
{
size_type __n = 0;
distance(__first, __last, __n);
if (size_type(_M_end_of_storage - _M_finish) >= __n)
{
const size_type __elems_after = _M_finish - __position;
iterator __old_finish = _M_finish;
if (__elems_after > __n)
{
uninitialized_copy(_M_finish - __n, _M_finish, _M_finish);
_M_finish += __n;
copy_backward(__position, __old_finish - __n, __old_finish);
copy(__first, __last, __position);
}
else
{
uninitialized_copy(__first + __elems_after, __last, _M_finish);
_M_finish += __n - __elems_after;
uninitialized_copy(__position, __old_finish, _M_finish);
_M_finish += __elems_after;
copy(__first, __first + __elems_after, __position);
}
}
else
{
const size_type __old_size = size();
const size_type __len = __old_size + max(__old_size, __n);
iterator __new_start = _M_allocate(__len);
iterator __new_finish = __new_start;
__STL_TRY {
__new_finish = uninitialized_copy(_M_start, __position, __new_start);
__new_finish = uninitialized_copy(__first, __last, __new_finish);
__new_finish
= uninitialized_copy(__position, _M_finish, __new_finish);
}
__STL_UNWIND((destroy(__new_start,__new_finish), _M_deallocate(__new_start,__len)));
destroy(_M_start, _M_finish);
_M_deallocate(_M_start, _M_end_of_storage - _M_start);
_M_start = __new_start;
_M_finish = __new_finish;
_M_end_of_storage = __new_start + __len;
}
}
}
template <class _Tp, class _Alloc>
vector<_Tp,_Alloc>& vector<_Tp,_Alloc>::operator=(const vector<_Tp, _Alloc>& __x)
{
if (&__x != this)
{
const size_type __xlen = __x.size();
if (__xlen > capacity())
{
iterator __tmp = _M_allocate_and_copy(__xlen, __x.begin(), __x.end());
destroy(_M_start, _M_finish);
_M_deallocate(_M_start, _M_end_of_storage - _M_start);
_M_start = __tmp;
_M_end_of_storage = _M_start + __xlen;
}
else if (size() >= __xlen)
{
iterator __i = copy(__x.begin(), __x.end(), begin());
destroy(__i, _M_finish);
}
else
{
copy(__x.begin(), __x.begin() + size(), _M_start);
uninitialized_copy(__x.begin() + size(), __x.end(), _M_finish);
}
_M_finish = _M_start + __xlen;
}
return *this;
}
还有两个比较相等和大小的函数模板：
template <class _Tp, class _Alloc>
inline bool
operator==(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
{
return __x.size() == __y.size() && equal(__x.begin(), __x.end(), __y.begin());
}
template <class _Tp, class _Alloc>
inline bool
operator<(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
{
return lexicographical_compare(__x.begin(), __x.end(), __y.begin(), __y.end());
}